1. Field of the Invention
This invention relates generally to magnetic recording hard disk drives (HDDs), and more particularly to a shingled magnetic recording (SMR) HDD that uses error-correction-code sectors associated with blocks of data sectors.
2. Description of the Related Art
Magnetic recording disk drives that use “shingle writing”, also called “shingled recording” or “shingled magnetic recording” (SMR), have been proposed, for example as described in U.S. Pat. No. 6,185,063 B1 and U.S. Pat. No. 6,967,810 B2. In SMR, the write head, which is wider than the read head in the cross-track direction, writes magnetic transitions by making a plurality of consecutive circular paths that partially overlap. The non-overlapped portions of adjacent paths form the shingled data tracks, which are thus narrower than the width of the write head. The data is read back by the narrower read head. The narrower shingled data tracks thus allow for increased data density. The shingled data tracks are arranged on the disk as annular bands separated by annular inter-band gaps or guard bands.
SMR HDDs may use error correction code (ECC) parity sectors for correction of errors in the data sectors. Sector-ECC has been proposed in SMR to enable ultra-high track densities with acceptable data sector failure rates. The writing of data to the data sectors in the shingled data tracks also includes the writing of error correction parity bits in the ECC sectors. The error correction bits in the ECC sectors are computed from the data to be written in the preceding block of data sectors, using an algorithm, like one of the well known ECC algorithms. When the data is read back from a sector the ECC detects errors and uses the error correction bits to correct the errors. However, sector-ECC increases the overhead of data that is used to ensure the integrity of the information and thus decreases the customer areal density. The strength of the ECC (the number of ECC sectors associated with a block of data sectors) is a global value of the HDD that is typically set during manufacturing based on factors such as the worst-case environmental condition, i.e., conditions which cause high track misregistration (TMR), or the intended use of the drive, e.g., short bursts of random data or long streams of data. However, the use of a fixed value for the number of ECC sectors that is too large can result in wasted disk space, and the use of a fixed value that is too small can result in data errors that cannot be corrected by the ECC.
What is needed is a SMR HDD that can adapt to changes in environmental conditions and type of data to optimize the strength of the ECC.